Cardivascular support control system

ABSTRACT

An apparatus for assisting cardiac function of a patient includes an inflatable chamber operably positionable with respect to an aorta of the patient, a percutaneous access device implantable with respect to a hypogastric region of the patient and connectible in fluid communication with the inflatable chamber, and a drive unit connectible through the percutaneous access device for selectively inflating and deflating the inflatable chamber in accordance with a control program stored in memory. The control program controls the drive unit in response to a periodically scheduled patient monitoring routine for measuring values of the physiology of the patient. The control program uses measured values as modified in accordance with the control program and physician programmable parameters for assisting cardiac function of the patient. The program includes the steps of automatically controlling the drive unit in response to a periodically scheduled patient monitoring routine for measuring values of physiology of the patient, and using measured values as modified in accordance with physician programmable parameters for assisting cardiac function of the patient. A software program is connectible in electronic communication with the control program for adjusting settings of the drive unit. The software program is capable of one or more of the following functions: retrieving current values of physician programmable parameters, selectively retrieving a history of the drive unit operation including error detection records, displaying a continuous ECG, and/or displaying a single-beat sample of aortic pressure waveform obtained in real time from the patient.

This application is a continuation-in-part of application Ser. No.09/164,513, filed Sep. 30, 1998, now U.S. Pat. No. 6,132,363.

FIELD OF THE INVENTION

The invention relates to a pressure control system for a cardiac assistdevice.

BACKGROUND OF THE INVENTION

Congestive heart failure is one of the major causes of mortality andmorbidity in the United States, affecting more than 2 million Americans.Pharmacologic therapy has prolonged survival and improved the quality oflife for many patients. For cardiac patients who do not respond toconventional treatments, heart transplantation is an effectivetreatment. However, the shortage of donor hearts limits its application.Mechanical assistance—in the form of the intraaortic balloon pump(IABP)—has become commonplace for the treatment of acute heart failure.But to date, no forms of mechanical assistance for chronic heart failure(CHF) are commercially available.

During the last decade, left ventricular assist (LVA) systems have beenused as a bridge to a heart transplant. These systems take over all thework of the heart and have been used for more than a year in manypatients who have then gone on to be transplanted. The success of thisprolonged cardiac support has led to ongoing clinical trials to evaluatethe use of LVA systems as an alternative to medical treatment.

SUMMARY OF THE INVENTION

The system is designed for use in selected patients with advancedchronic congestive failure no longer responsive to pharmacologicmanagement. Like the intraaortic balloon pump (IABP), the presentinvention is a left ventricular assist (LVA) system that providesdiastolic augmentation to the failing left ventricle. However, thepresent invention differs from the IABP in a number of respects. Thepresent invention is intended to remain in the body indefinitely,providing long-term cardiac support as an alternative to medicaltreatment. It is not a bridge to a heart transplant. Patients will bedischarged from the hospital, live at home, and resume many normalactivities.

The system consists of: the blood pump, an inflatable bladder suturedinto the wall of the descending thoracic aorta, the percutaneous accessdevice (PAD), a through-the-skin port that allows power and electricalsignals to pass between the drive unit and the blood pump, and theexternal drive unit, which powers and controls the blood pump.

The blood pump has only one moving part—a diaphragm—and no valves. Thepump has a stroke volume of up to 60 cc. To inflate the blood pump,pressurized room air is supplied from a wearable (<5 lb.)battery-powered unit or a larger drive unit powered by householdelectricity. The air reaches the blood pump through an external driveline, attached to the drive unit, and an internal drive line implantedin the patient. The internal and external drive lines connect to eachother through the percutaneous access device. The PAD also serves as aconduit for electrical signals that are transmitted from the heart tothe drive unit through electrical leads.

Like the intraaortic balloon pump (IABP), a device whose effectivenessin providing circulatory support for days to months is well accepted,the present invention operates on the principle of diastolicaugmentation. The system inflates the blood pump during diastole anddeflates it just before systole. When deflated, the pump conforms to theinner wall of the aorta, functioning as a passive aortic graft.

In a patient with left ventricular failure, diastolic augmentationreduces left ventricular afterload and improves coronary perfusion. Thisleads to improved myocardial oxygen supply and demand balance. While thesystem takes advantage of the same operating principle and anatomiclocation as the IABP, the larger stroke volume of the present inventionis expected to yield improved hemodynamic benefits. Unlike the IABP,which is designed for short-term, in-hospital treatment, the presentinvention is designed for long-term circulatory support of the CHFpatient who will return home after recovering from implant surgery.

During the last decade, left ventricular assist (LVA) systems have beenused as a bridge to a heart transplant. These systems are designed totake over all of the work of the left ventricle. In contrast, thepresent invention requires that patients have some functioningmyocardium and can benefit from diastolic augmentation. Several featuresset the system apart from other LVA systems designed for long-termsupport:

It is an “on demand” system. The present invention can provide eithercontinuous or intermittent cardiac support, according to the physician'sdetermination of the patient's needs. When the system is turned off, thepatient does not need to be connected to the machine. Because other LVAsystems are designed with valves, they must operate continuously toavoid the pooling of blood, which leads to thrombosis and emboli. Thepresent invention can operate intermittently because it has no valves.Long-term tests of the present invention and its predecessors indicatethat turning the assist device on after it has been off for some timedoes not result in emboli.

Patients will not be on anticoagulant therapy. The blood-contactingsurface of the present invention is textured to encourage tissueingrowth. Its biocompatibility has been confirmed in calf studies inwhich the blood pump was activated intermittently for periods up to 25months. No surgical alteration of cardiac anatomy is necessary, so nofunctioning myocardium is removed when the present invention isimplanted.

Following the success of LVA systems as a “bridge to transplant” in thepast decade, trials are underway to evaluate these systems for long-termuse as an alternative to medical treatment in CHF. A number ofcardiomyopathy patients have recovered sufficiently to be removed fromthe transplant list and to have the LVA system removed. LVA systems aretherefore also becoming known as a “bridge to recovery.” The presentinvention is not a direct competitor of these LVA systems. Rather, it isone of a family of mechanical support devices, each designed forparticular patient needs. In the future, physicians will be able tochoose from various models to provide the best match for each patient.

Electrode leads from electrodes are projected through the skin via thepercutaneous access device (PAD) and the R wave of the electrocardiogramis monitored to control the fluid pressure during inflating anddeflating cycles of the pump in synchronism with the natural heartbeatactions. By inflating the cardiac assist device during diastole anddeflating the device during systole, the load on the left ventricle isreduced and the aortic pressure is raised to increase the blood flow tothe coronary arteries. The cardiac motion needs to be sensed accuratelyto enable the device to be inflated and deflated correctly in accordancewith the cardiac cycle. One way to sense cardiac motion is to measurethe aortic pressure wave form and determine the occurrence of thedicrotic notch, which indicates when the aortic valve closes. It isdesirable in the present invention to provide an apparatus and methodfor accurately sensing the blood pressure wave form within the aorta. Itis desirable in the present invention to control the inflation anddeflation timing of the blood pump or other cardiac assist device byperiodically monitoring the aortic pressure while still providingpartial cardiac assistance during the patient monitoring procedure tolessen the impact on the patient, and permit more frequent monitoringprocedures to be performed. The monitored aortic pressures are stored,and the operational parameters of inflation and deflation timing of theblood pump for each subsequent heartbeat are adjusted in accordance withthe stored aortic pressure.

According to the present invention, control means is provided formeasuring arterial pressure of the patient during a monitoringprocedure, sometimes referred to as a scheduled pressure measurement.The control means provides for adjusting the inflation and deflationtiming of the pump for subsequent heartbeats in accordance with aprogram stored in memory of the control means based on the arterialpressure measured during the scheduled pressure measurement. Gashandling means is provided for inflating and deflating the pumpingbladder in accordance with the evaluation of the arterial pressuremeasured by the control means.

The inflatable chamber of the cardiac assist device is disposed in adesired location with respect to the aorta of the patient. Afterconnection of the inflatable chamber of the cardiac assist device to thedrive means, a patient monitoring procedure is conducted to obtain apressure measurement of the aortic pressure wave form. During theprocedure, the inflatable chamber of the pump is first inflated toprovide cardiac assistance during the monitoring procedure, and thenpartially deflated with the control means controlling the volume offluid expelled from the inflatable chamber to provide a partiallyinflated chamber. The volume of gas expelled from the pump is calculatedby monitoring the pressure drop across the deflation valve over aninterval of time.

Accumulating the pressure drop with respect to time provides a valuecorresponding to the total volume of gas expelled from the pump. Thetotal volume is monitored so that a predetermined volume is leftremaining within the inflatable chamber. When the cardiac assist deviceis partially filled with gas, the deflation valve is closed to isolatethe pump from the drive means while in a partially inflated condition.The pressure of the gas in the chamber reflects the aortic pressure ofthe patient when partially inflated and isolated from the drive means.This state is preferably maintained for at least a partial heartbeat andpreferably at least one complete heartbeat. The pressure of the chamberis monitored continuously by a pressure sensor in the control means forthe heartbeat cycle being monitored. A wave form of the aortic pressureof the heartbeat cycle is stored in memory of the control means. At thesame time, an ECG signal is monitored and stored in memory of thecontrol means. During the patient monitoring procedure, the controlprogram stored in memory of the control means computes the systolic timeinterval, which is the elapsed time from the beginning of the QRS waveof the ECG signal to the closing of the aortic valve as indicated by thedicrotic notch of the aortic pressure. The ventricular assist controlprogram uses the information provided during the patient monitoringprocedure to adjust the inflation volume and timing for subsequentheartbeats. The patient monitoring procedure is repeated at scheduledtime intervals and/or with changing heart rate conditions. The timedintervals and/or heart rate parameter conditions are fully programmableby the attending physician within preselected ranges and are stored in apatient parameter table located in memory of the control means.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art when the followingdescription of the best mode contemplated for practicing the inventionis read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawingswherein like reference numerals refer to like parts throughout theseveral views, and wherein:

FIG. 1 illustrates the system according to the present inventionincludes the blood pump, the PAD, and the drive unit;

FIG. 2 illustrates the blood pump;

FIG. 3 illustrates parts of the percutaneous access device (PAD)according to the present invention;

FIG. 4 illustrates the PAD as implanted through the skin;

FIG. 5 illustrates the implanted part of the percutaneous access devicewith the internal drive line and pacing leads attached to the threeterminals at the left;

FIG. 6 illustrates a diagram of the line-powered drive unit (LPDU)showing positions of switches, and indicator lights;

FIG. 7 is a main menu structure of the Win MAV Communications software;

FIG. 8 is a screen shot of a sample measurement window and cursors;

FIG. 9 is a graph of an aortic pressure wave form versus time during apatient monitoring procedure of a cardiac cycle compared to analternative pressure measurement procedure; and

FIG. 10 is a specified flowchart illustrating program steps to partiallydeflate the cardiac assist device during a patient monitoring procedure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

At the start of the noninvasive screening process, a skin biopsy will betaken and cells cultured onto the implantable part of the PAD. In cellculture, the patient's fibroblasts extend cell processes into thenanoporous PAD neck. Soon after PAD implantation, host fibroblasts forma meshlike, collagenous structure with the fibroblasts that already havecoated the neck. This creates a biological seal which inhibitspenetration by infectious organisms.

About one week before the implantation of the blood pump, the PAD willbe implanted. In this surgical procedure, a transverse skin incision ismade at the level of L₁₋₂ of the left hypogastric region. From thisincision a subcutaneous pocket 10 cm in diameter is created, and acircular incision is made in the skin covering the pocket. The PAD isinserted through the transverse incision into the subcutaneous pocketand exposed through the circular incision. Care is taken to avoidcontact with the PAD fibroblast coating. The pocket is closed usingProlene sutures.

During the healing process, the PAD becomes stabilized by scar tissue.It is essential, therefore, to minimize movement of the PAD site afterinsertion.

Before induction of anesthesia, ECG, IV lines and a urinary catheterwill be introduced. Angiographic catheters will be inserted in the rightradial artery and left femoral artery for proximal and distal arterialpressure monitoring. The patient will be induced and intubated.Anesthesia will be maintained via inhalant anesthetic (Isoflurane). ASwan-Ganz catheter will be inserted via the left jugular vein and passedinto the pulmonary artery for monitoring PAP, PCWP, CO, and CVP. Bloodgases, Hb, ACT, and Hct will be monitored during surgery.

The blood pump will be inserted through a left thoracotomy approach.Following heparinization, the patient will be placed on coronary arterybypass. The aorta will be cross clamped above and below the intendedimplant site using a staged technique. With the help of a template, alongitudinal incision will be made in the anterior aortic wall. Theblood pump will then be sutured to the edges of the opening created bythe incision and the cross clamps removed.

The drive unit will be temporarily connected to the blood pump to verifythat the pumping membrane is intact and has not been damaged duringinsertion. Any suture line leaks or discontinuities will be repaired.The patient will be weaned from bypass and heparinization will bereversed with Protamine. Two pacing electrodes will be placed on theepicardium of the left ventricle. With the help of a tunneling device,the internal drive line will be brought from the thoracic cavity to thePAD. Through a separate tunnel the pacing electrodes will be passed fromthe pocket to the thoracic cavity and attached to the ends of the bloodpump. The blood pump will be reconnected to the drive unit through thePAD. Two chest tubes will be placed into the thoracic cavity, oneanterior and one posterior and connected to an underwater seal. Thethoracic cavity will then be closed in layers. The complete system isshown in FIG. 1. The blood pump 10 is an approximately 6.5-inch longpolyurethane bladder illustrated in FIG. 2 and is sutured to the edgesof an incision of matched size in the wall of the descending thoracicaorta. The pump is inflated with filtered room air supplied from thedrive unit. The blood pump can be adjusted for full or partialinflation.

The internal drive line is a kink resistant, 5 mm ID tube that extendsfrom the implanted blood pump to the PAD 12. It provides a pneumaticconnection between the blood pump and the PAD. Two standard pacemakerleads are implanted in the patient's epicardium during the blood pumpimplantation and brought through a subcutaneous tunnel to the PAD. Theseleads sense the electrocardiogram and conduct it to the drive unit,which processes the signal to identify the R wave. The R wave triggersinflation and deflation of the blood pump.

The PAD has two main parts as illustrated in FIG. 3: (1) an implanted,0.75″ diameter cylindrical neck with a flexible, cloth-covered flange ata base 16, precoated with fibroblasts and implanted about a week beforeblood pump insertion, and positioned near the patient's navel, with theflange under the skin, and inside the neck is a replaceable turret; and(2) an external, detachable part 18 which connects the PAD to the driveunit 14.

Patients can be provided with two drive units: (1) the Line-poweredDrive Unit (LPDU) operates continuously on household current, has backupbatteries capable of nearly 3-hour service, is intended mainly for usewhen the patient is stationary, either seated or lying, and is housed ina wheeled suitcase; and (2) the Wearable Drive Unit (WDU) is intended tobe used once or twice daily, not for continuous use, can run nearly 2hours on one set of batteries, allows the patient to move freely whilereceiving cardiac support, and can be worn or carried away from home forstandby use.

Both drive units control blood pump inflation and deflation timing andautomatically adjust the timing for changes in heart rate. The units canbe programmed, under a physician's direction, to tailor blood-pumpoperation to each patient's cardiac function. This is done via PC-basedsoftware.

Safety features are built into each drive unit to protect the patient ifthe system fails. For example, the drive unit's motor and valves willshut down in case of a software failure. When this happens, the bloodpump deflates and remains safely deflated. To make sure that the WDUdoes not operate erratically when its batteries get low, the systemmonitors battery voltage. When voltage drops below a certain level, thesystem makes sure the valves and motor are in a safe state and thenshuts itself down. The LPDU is capable of detecting a pinhole leak inthe blood pump should one develop. The WDU is not. For this reason, theLPDU should be used most of the time and the WDU only occasionally andfor short periods.

The drive unit (either the LPDU or the WDU) automatically adjusts bloodpump inflation and deflation timing based on: (1) comparison of theduration of any R—R interval (except the first) with its predecessors;(2) periodic aortic pressure measurement; (3) determination of the Q-S₂interval; and (4) application of an Inflation Adjustment factor, definedby the physician.

In addition, a number of parameters can be programmed according to thephysician's directions. Each of the programmable parameters has adefault setting, stored in the drive unit's Patient Parameter Table(PPT) (See Table 1). These settings can be modified to obtain themaximum benefits of diastolic augmentation for a given patient. Each ofthe programmable parameters is discussed in further detail below.

Changes in the patient's clinical status or medications can affect LVcontractility, coronary artery blood flow, and LV end-diastolic volumeand pressure. These changes may, in turn, affect the timing of inflationand deflation. Therefore, any change in medications or significantchange in clinical status requires a reassessment of the PPT. settings.

The same software program that is used to adjust the drive unitsettings-can also retrieve the current PPT settings and a history of theunit's operation. The software also can display a continuous ECG andsingle-beat samples of aortic pressure waveforms obtained in real timefrom the patient.

TABLE 1 Summary of Patient Parameters PARAMETER UNITS MINIMUM DEFAULTMAXIMUM Scheduled Pressure min 3 10 20 Measurement Pressure Measure- sec15 30 60 ment Lock-Out NSR Deviation % 10 20 80 Inflation Adjustmentmsec* 0 28 50 Deflation Adjust- msec* 0 0 80 ment Arrhythmia Thres- % 510 15 hold Arrhythmia Inflate msec* 250 400 420 Delay Dicrotic Notchmsec* 150 180 200 Earliest (DNE) Dicrotic Notch msec* 300 350 420 Latest(DNL) Dicrotic Notch msec* DNE entry 300 DNL entry Default Filling Timemsec* 60 128 160 Stroke Volume % 25 100 110

Periodically, the drive unit interrupts counterpulsation for two cardiaccycles to obtain an aortic pressure waveform from which the Q-S₂interval is measured. This method of measuring and processing thecentral aortic pressure is called a partial cycle. The drive unit usesthe measurement to adjust inflation timing of the blood pump, as theheart rate and hemodynamic state of the patient changes. The timing isalways further modified by the Inflation Adjustment value, which isspecified by the physician. The interval between Q-S₂ measurements isbased on the NSR Deviation, a programmable value that representspercentage changes in heart rate. However, the physician can prescribethe maximum and minimum intervals between measurements by adjusting theScheduled Pressure Measurement and. Pressure Measurement Lock-Outsettings. The Scheduled Pressure Measurement setting determines themaximum time between measurements. The Pressure Measurement Lock-Outsetting controls the minimum time between measurements.

As long as an intra-arterial catheter is in place, the drive unitoperator must ascertain the patient's arterial pressure waveform andmanually change inflation and deflation adjustment settings until thedesired assist waveform is obtained. For example, the blood pump mightbe set to begin inflating just after the dicrotic notch and to begindeflating at the end of diastole. Once the intra-arterial catheter isremoved, it will no longer be possible to base timing adjustments ondirect arterial pressure waveform measurements. For that reason,pressure waveform data must be recorded over a range of heart rates andphysiological conditions while the catheter is in place. These data willserve as a guide for future timing adjustments, after the catheter hasbeen removed. Additional reference measurements should be made any timean intra-arterial catheter is placed subsequently, such as during acardiac catheterization.

As discussed above, blood pump inflation timing is determined by Q-S₂and the Inflation Adjustment setting programmed into the drive unit. IfQ-S₂ changes, the previously programmed Inflation Adjustment setting mayno longer be appropriate, and the physician must adjust it. Referencetiming data gathered when the patient had an indwelling arterialcatheter should be used as a guide in making new Inflation Adjustmentsettings.

In adjusting settings, the physician must consider that: (1) the Q-S₂interval will change, depending on whether the measured cardiac cycle isassisted, unassisted for a few beats, or unassisted for more than a fewbeats (the partial cycle measurement can be obtained only from anunassisted beat that follows an assisted beat); (2) the patient receivesno hemodynamic support during the partial cycle; and (3) the patientmust be in normal sinus rhythm immediately preceding partial cyclemeasurements. If the patient is not in stable sinus rhythm, aorticpressure will not be measured during the partial cycle, and the driveunit will base timing on a programmable value, the Arrhythmia InflateDelay.

The frequency with which partial cycle measurements are made is a matterof clinical judgment. Frequent measurement allows better tracking ofchanges in the patient's condition, but the cost is two cardiac cyclesduring which the patient receives no left ventricular assistance.

At every beat, the drive unit calculates the percentage change betweenthe current R—R interval and the R—R interval measured in the previouspartial cycle. The percentage change is the NSR (Normal Sinus Rhythm).If the NSR exceeds the NSR Deviation value prescribed by the physician,the drive unit makes a new partial cycle measurement.

Ejection time of an unassisted cardiac cycle is longer than that of anassisted cardiac cycle. Inflation Adjustment is a physician-determinedtime interval added to Q-S₂ to compensate for that phenomenon. TheInflation Adjustment setting also allows adjustments to be made formechanical factors that affect timing. The default setting of theInflation Adjustment causes blood pump inflation to begin at thepredicted time of appearance of the dicrotic notch, based on the mostrecently measured Q-S₂. A negative Inflation Adjustment value causesblood pump inflation to start a specific amount of time before thepredicted occurrence of the dicrotic notch. Conversely, a positiveInflation Adjustment value delays blood pump inflation a specific amountof time after the predicted occurrence of the dicrotic notch.

If the decision about Inflation Adjustment settings is being based onreference data collected when the patient's physiologic/clinical statuswas different, the physician must consider how the patient's currentclinical status will affect optimal timing adjustments. If the InflationAdjustment setting delays blood pump inflation too long after thedicrotic notch, suboptimal coronary perfusion results. Conversely, earlyblood pump inflation could lead to premature aortic valve closure and/oraortic regurgitation with resultant reduction in LV stroke volume. Thephysician must determine the risk-benefit ratio of the inflationadjustment for a patient at any given time in the patient's clinicalcourse.

The Deflation Adjustment parameter sets the time interval betweendetection of the upstroke of the R wave and initiation of blood pumpdeflation. If the Deflation Adjustment setting is at its default valueof zero, the blood pump will deflate 20-30 msec before the QRS.Increasing the Deflation Adjustment value delays deflation, therebyprolonging the period of blood pump inflation.

Like Inflation Adjustment, the Deflation Adjustment setting should bealtered only on the basis of the patient's reference data. Prematuredeflation may reduce coronary artery blood flow. Late deflation mayresult in suboptimal reduction in left ventricular afterload. Thephysician must determine the risk-benefit ratio of deflation timingadjustments.

During any arrhythmia, the partial cycle measurement has littlepredictive value. Therefore, when the drive unit senses an arrhythmia,it suspends partial cycle measurements for 15-60 seconds. During thisperiod, it bases timing on a physician-selected value (the ArrhythmiaInflate Delay value) instead of on the Q-S₂ interval.

The Arrhythmia Threshold setting allows the physician to adjust thedrive unit's “sensitivity” to arrhythmias. To determine if there is anarrhythmia, the drive unit calculates an arrhythmia index for eachcardiac cycle. The arrhythmia index is defined as: (average D over nbeats (R—R)/average R—R over n beats) 100%, where n is 8 or 16 beats,D=absolute change, and (R—R)=measured R—R interval. If the resultexceeds the Arrhythmia Threshold setting selected by the physician, thedrive unit switches to a default mode. In default mode, the followingconditions exist:

(1) The Deflation Adjustment is set to zero. In this state, the bloodpump will automatically deflate whenever it senses the upstroke of the Rwave.

(2) The Arrhythmia Inflate Delay replaces the Q-S₂ interval.

(3) The Inflation Adjustment is added to the Arrhythmia Inflate Delay.

The above default settings result in early deflation and late inflationof the blood pump. These timing settings are conservative in order tominimize chances of adverse events. The conditions defined by thearrhythmia default mode will continue for as long as the physician hasspecified with the Pressure Measurement Lock-Out setting.

As discussed above, the drive unit replaces the measured Q-S₂ intervalwith the Arrhythmia Inflate Delay value when it senses an arrhythmia. Ineffect, the Arrhythmia Inflate Delay functions as a default Q-S₂. Underthese conditions, the Inflation Adjustment setting remains in effect.The Arrhythmia Inflate Delay value should be selected on the basis ofthe patient's arrhythmia history. If the patient has any persistentarrhythmia, a pacemaker should be considered, as it will allow moreeffective LV assistance.

To detect the dicrotic notch, the drive unit uses an algorithm thatinspects the aortic pressure waveform, within a physician-prescribedtime window. If a dicrotic notch is not detected within this window, thealgorithm uses a physician-prescribed default value for the location ofthe dicrotic notch.

The window is defined by a beginning point (Dicrotic Notch Earliest, orDNE) and an end point (Dicrotic Notch Latest, or DNL). The physiciansets both values in reference to the onset of the R wave. The physicianalso sets a default value, the Dicrotic Notch Default, to be used if thealgorithm cannot locate a dicrotic notch within the prescribed window.All three above parameters must be coordinated. That is, the DNE valuemust be less than the DNL value, and the default value must lie betweenthe DNE and the DNL values.

The algorithm may mistake an artifact for the dicrotic notch. Making thewindow narrow decreases the likelihood of this happening. But if thewindow is too narrow and does not include the dicrotic notch, the driveunit will use the default setting, rather than the actual dicroticnotch. Conversely, making the window wider allows tracking the dicroticnotch over a wider range of heart rates, but also increases thelikelihood of mistaking an artifact for the notch. To find out if thealgorithm is using the actual dicrotic notch, an artifact, or thedefault setting, use the PC-based software.

The size of the window should also reflect variations in the patient'sQ-S₂ over time and over different hemodynamic conditions.

The Filling Time setting establishes a target value for the rate ofblood pump inflation. However, it is recommended that the default valuebe used. The default value takes into account numerous constraints thatare necessary to maintain appropriate and safe pressure gradients. Inpractice, these constraints have priority over meeting the Filling Timetarget value.

Over-inflating the blood pump may shorten its lifespan.

Therefore, there are built-in limitations to the pressure and strokevolume that can be delivered to the blood pump. A Stroke Volume settingof 100% delivers a stroke volume of 50-55 cc. The Stroke Volume can beadjusted to deliver from 25% to 110% of full stroke volume. It isrecommended that stroke volume not exceed 100% for more than 2-3 days.Note that such a setting may require a change in the Assist PressureCorrection Factor.

Blood pump stroke volume should not exceed the LV stroke volume. Ifblood pump stroke volume is set higher than LV stroke volume, and ifdeflation is well-timed, then blood pump deflation may “steal” bloodfrom the coronary and other arteries.

In the immediate post-operative period (2 weeks), stroke volume shouldbe set no higher than 60% to reduce peak assisted pressure and resultingstress on the fresh suture line. After the sutures have stabilized,stroke volume may be increased.

The system detects pacemaker spikes and rejects them as QRS complexes.In addition, over a course of 16 cardiac cycles, the system learns theshape and size of the tail that follows the pacemaker spike andsubtracts it from the ECG signal. This allows for better detection ofthe QRS complex when the tail and the real QRS are superimposed.However, if the patient has a dual chamber pacemaker, the algorithm willaverage the two potentially significantly different tails. This mayconfuse the pacemaker detection algorithm and may require reprogrammingof the pacemaker.

Two alarms warn of excessive pressure in the blood pump. One alarm isactivated whenever pressure in the drive line reaches 260 mm Hg. Thesecond alarm is programmable. It is activated when the pressure in thedrive line exceeds systolic blood pressure by an amount the physicianhas selected. If this alarm is set at its default value of zero, thealarm threshold is 80 mm Hg above systolic pressure. By adjusting theAssist Pressure Correction Factor, the alarm threshold may be increasedby up to 50 mm Hg or lowered by as much as 20 mm Hg, resulting inthresholds of 60 to 130 mm Hg above systolic pressure.

In general, the threshold should be as low as possible, without causingfalse alarms or interfering with good pumping. The threshold can beincreased if the unassisted peak systolic pressure is low or if theblood pump is being operated above the 100% Stroke Volume setting. Underthese conditions, the difference between systolic pressure and pumppressure will be sufficient to activate the alarm unless the thresholdhas been increased. The default setting is appropriate in most othersituations.

Closed-chest defibrillation poses no risks to the blood pump. If CPRmust be performed within the first few days after surgery, damage to thesuture line is possible. During this same period, any medication thatincreases systemic blood pressure to an abnormally high level may alsodisrupt the suture line. The augmented blood pressure during these fewdays should be at the lowest level compatible with the patient's wellbeing, so as not to risk disrupting the suture line.

Counterpulsation should be temporarily suspended during CPR because ofthe inherent inability to synchronize the assist device to chestcompression. However, as soon as a rhythm is re-established andcounterpulsation with correct timing can be implemented, the blood pumpshould be restarted.

Despite the difficult conditions of resuscitation, personnel shouldattempt, if possible, to prevent mechanical stress to the percutaneousaccess device, as this could result in disruption of the access devicetissue adhesion and lead to infection.

Recall that the PAD 12 has three main parts as illustrated in FIG. 4:(1) a cylindrical neck 20 with a flange 22 at the bottom, implanted sothat the neck protrudes through the skin 24; (2) a replaceable turret 26inside the neck; and (3) an external part 18, which connects to thedrive unit's external drive line. The PAD is positioned near thepatient's navel. During the implantation procedure, an internal driveline 28 from the blood pump and the pacemaker leads 30 from theepicardium are connected to the implanted part of the PAD as illustratedprior to implantation in FIG. 5.

The LPDU is housed in a wheeled suitcase with a retractable handle and atop view is illustrated in FIG. 6. It uses household current (110-voltAC). It also contains backup batteries for short-term operation in caseof a power failure. Attached to the suitcase is a pouch where theexternal drive line can be stored when not in use. When the externaldrive line is stored in the pouch, the PAD connector should be snappedonto the ball inside the pouch. Instructions can also be stored in thepouch.

The LPDU is designed to be used mainly when the patient is resting in achair or bed. The physician may allow the patient to walk a shortdistance, wheeling the LPDU on a hard, level surface. The LPDU has sevenindicator lights, shown in FIG. 6. The blue “AC ON/OFF” switch 32 turnson power to the drive unit, but it does not activate pumping. The green“PUMP ON/OFF” switch 34 must be pressed to start the pumping process.The orange “BATTERY LOW” light 36, red “CHECK CONNECTION” light 38, andred “REPLACE DRIVE” light 40, along with different patterns of beeps,alert the user to problems. The charge level of the LPDU's built-inbackup batteries is tested by pressing the orange “BATTERY STATUS”button 42 while the “AC ON/OFF” button is in the “OFF” position. If allfive of the orange “BATTERY LEVEL” lights 44 come on, the batteries arefully charged. The LPDU also has a light inside the plug at the end ofits power cord. The light glows when the cord is plugged into a liveoutlet.

The present invention includes software for use in conjunction with adrive unit of the system. The following description of the softwareincludes details of the user interface, operational, and safety andsecurity requirements. The software also contains a Help file.

The software is specific to the drive unit electronics and will notoperate with other versions of the hardware. The device hardware whichmay be referred to throughout this text includes the following:Mechanical Auxiliary Ventricle Rev. 3.0 (MAV) and Components: WearableDrive Unit (WDU); Line Powered Drive Unit (LPDU); External Drive Line;Percutaneous Access Device (PAD); and Blood Pump. The Personal Computer(PC) software is referred to as WinMAV.

The software product provides straightforward access to a Drive Unit, aswell as offers data storage and analysis options. All operations aremenu driven. Navigation through the menu hierarchy uses standardkeyboard and mouse functions for user friendliness. In addition, helpscreens and status bars are provided to reflect menu functions.

The software is designed to monitor the patient ECG (and other signals)in real time. However, the software is not intended as a patientmonitor, due to the specific requirements of the drive unit hardware, aswell as the non-standard cardiac leads. In addition, these signals maybe stored and reviewed at a later date. As such, data scrolling,storing, and analysis tools are provided as part of the software design.

The software product also monitors device operating parameters at anumber of different times. Such parameters can be stored in the driveunit memory, retrieved from the unit while pumping, or stored to diskand reviewed at a later time. In addition, the software will enableoperating parameters to be adjusted and a number of direct operatingcommands to be issued.

The remaining part of this description contains information on thegeneral function of the WinMAV software. It describes basic systemconfigurations as well as detailed requirements. A general descriptionand overview are provided below.

Data Security and Integrity Requirements describes the protocol requiredfor accurate and secure communications between the PC and drive unit. InMenu Structure and Data Storage, detailed requirements of menuhierarchies are presented both in the text and graphically. In addition,directory and file naming schemes as well as menu navigation rulesapplicable to all menus are discussed. Finally, detailed requirementsfor all menu functions are presented in DU Control Menu Functions.

The PC can be connected to either a wearable or line-powered drive unit,which is part of the overall Mechanical Auxiliary Ventricle (MAV)system. A brief overview of the device is presented in this section toprovide perspective on the computer interface and device control.

The purpose of the MAV system is to provide diastolic augmentation topatients who display low cardiac function or cardiac deficiency. It istargeted to be a permanent, implanted cardiac assist device driven by anexternal system including an embedded computer, a compressor, areservoir, solenoid valves, pressure sensors and signal conditioningcircuits. The line powered drive unit incorporates a second reservoirand isolation chamber. The software for the drive unit is flexibleenough to manage patient to patient variations in ECG and blood pressureprofiles, which are taken into account during the calibration modes ofthe unit. The ECG is monitored continuously and is used as a triggerwhereas the patient blood pressure is monitored periodically. Afterthese pressure measurements, which are made on both a fixed interval andupon the detection of changing patient conditions, timing parameters ofthe pump are updated.

The unit functions independently from other instrumentation, and theline powered unit automatically switches to DC operation upon line powerfailure or disconnection. The software performs a self test immediatelyupon power-up and begins the pumping sequence after performing apurge/fill cycle (in the case of the line-powered unit) and an aorticpressure measurement.

All modes of operation are designed to keep the transmembrane pressurebelow 80 mm Hg. Should the pressure rise above the safety margin for theblood pump or if data is not within specified limits, the system entersa safe power down mode. Watchdog timer provisions are also made in bothhardware and software to recover from any system error which may causethe CPU to enter an undefined state. In addition to shut down and alarmstates, error conditions are recorded in the device's non-volatilememory.

The PC communications software (WinMAV) provides the authorized useraccess to the drive unit for both interrogation and control of devicefunction. During factory development and final preparatoryinitialization of the device, WinMAV provides a means to ensureelectrode and sensor integrity as-well as evaluate overall devicefunction.

After the patient is equipped with the unit, the WinMAV softwareprovides the clinical staff a means to periodically monitor thepatient's condition as well as the device history. In addition, it isthe WinMAV software which will allow the staff to adjust deviceoperating parameters, which are patient dependent, and then monitor theeffects of changing these parameters. The recording and file savingfeatures of the software also provide a means of tracking the history ofboth the patient's condition and the device operation over an extendedperiod of time.

Given the critical nature of the patient parameter adjustment, serialcommunication of WinMAV will follow standard extended RS-232 protocolwith the addition of several layers of protection to guard againstunauthorized access to the device. While data integrity is protectedwith the stringent communications checking schemes, security is ensuredby both a physical connection to the device which is a non-standardproprietary connector and communications command sequences which areencoded. In addition, all users qualified to alter the patient table areissued a Password for authorization on the PC. Finally, the softwareprotects against erroneous parameters by rejecting any attempt by theuser to enter values which fall outside pre-determined safety limits.

The software restricts user access. Communications protocols aresufficient to ensure data integrity and security. Drive unitidentification is checked prior to any access. In addition, the softwarewill ensure that all modified patient parameters fall within pre-definedacceptable ranges of safety.

Three levels of user access are defined in Data Security and IntegrityRequirements. Level 1 allows viewing of recorded data files only. Level2 access allows modification of operating parameters necessary to treatthe patient on a daily basis. The third level of access is morestringent and shall be referred to Level 3 access. This level isrequired to minimize inadvertent changes to settings that should befactory adjustable only.

The authorized user is able to view patient signals from the drive unit.These signals may be recorded and stored to disk during the real timedisplay, and the user can freeze the display and perform measurements onany of the displayed waveforms.

The drive unit software continuously updates a snapshot buffer of themachine state and several physiologic parameters. A number of errorconditions result in drive unit storage of this snapshot at differenttimes during operation. The software allows the authorized user todownload, view, and store these records to disk as well as view currentoperating conditions.

The parameters in the patient table in the drive unit memory are used toset operating parameters as well as determine physiologic conditionssuch as an arrhythmia or deviation from normal sinus rhythm. Thesoftware allows the authorized operator to access, retrieve, and updatethe patient parameter table while ensuring that safe limits of theseparameters are maintained.

The physician or other authorized operator can execute drive unitoperating commands directly from the PC. The software also allows memoryresets during factory updates or normal operating mode. A full driveunit reset to factory defaults requires Level 3 access.

The software allows the operator to review previously recorded datastreams. Much of the off line processing functions are similar to thoseunder real time control. These include freeze frame and measurementscreen display modes.

Also, there are functions for storing data to disk in a formatcompatible with current database programs.

The software requires, as a minimum, a 120 MHZ Pentium PC with 16 MBytesRAM. Hard disk space requirements are based on the number and length ofreal-time records to be saved. In addition, the operating system shallbe Windows 95, Windows 98, or Windows NT.

The extended RS-232 protocol ensures integrity of data transfer. Theother layers of security described in Data Security and IntegrityRequirements protect against unauthorized device access. Hard codedsafety limits to device parameters ensure a safe operating environmentfor the patient in terms of device settings. The drive units providemultiple layers of hardware and software safety design techniques foradded protection.

An operator can access data and issue selective commands to the driveunit at any time during operation. The link is made from a local PCrunning the WinMAV software. Alternatively, the connection can be madevia modem which requires that the physician instruct the patient on theconnection procedure over a separate phone line. In either case, serialcommunication follows standard RS-232 protocol with the addition ofseveral layers of security protection including user name and passwordauthorization on the PC.

There are three levels of security access to the system.

Each succeeding level requires additional information from the user, andis therefore more difficult to access. The levels are described indetail as follows:

Level 1: No security protocol is required for access. The user name andpassword are not required. The only function available is the viewing ofstored data files on disk.

Level 2: The required access codes include all three data items, whichinclude the user name, password, and machine ID. This level of accessallows the physician or technician access to all normal modes ofoperation. This includes all previously mentioned functions as well asreal time display, command functions, parameter table modifications, andhistory record and snapshot information. This level also enables theuser to reset the event log, which automatically makes a copy of therecord to disk. Finally, the user may set the drive unit to a pacemakertrigger mode, which ignores the normal QRS signal. The latter commandmust only be done under physician approval and under given specificcircumstances.

Level 3: This level of access is meant for factory authorized personnelonly, and is accessed by use of a specific machine ID. The functionsthat may be accessed include stroke volume calibration, and execution ofthe Reset DU (reset the drive unit) command.

An additional mode that is outside the normal access levels allowsupdates of authorized users. A separate password allows an authorizeduser to modify the list of personnel allowed to access the drive unitand modify their passwords.

All command functions are menu and/or tool bar driven for user ease. Thestructure of the menu hierarchy is presented in FIG. 7. The menuselections appear at the top of each screen, similar to other Windowsprograms. Directly below the main menu, the tool bar is available toautomate more frequently used tasks. The user can scan menu selectionsusing designated keys or a mouse. Unless the PC is occupied with realtime data update and display, a help button is provided to describe menucommand functions. In this section, top-down menu structure overview andnavigation rule specifications are furnished.

The top level menu functions are accessible via the keyboard or themouse via a pull down menu structure. Left and right arrow keys, the<enter> and <escape> keys, <alt>+ keyboard keys (underlined letters onthe menu), mouse movement and both mouse buttons control programexecution.

Alternatively, pressing the left mouse button while positioned on anytool bar button results in command execution. Positioning the cursorover any tool bar button (without left clicking) opens a small textwindow which describes the button. Also, a more verbose description isgiven at the bottom left portion of the screen.

Specific menu functions are presented in DU Control Menu Functions.Keyboard and mouse actions result in accessing the functions shown. Thehighest level menu items separate the WinMAV functions into thefollowing five categories:

(1) File: Device error statistics and real time data files can beviewed, stored to disk, and printed from this menu. Additionally,several functions for database compatibility are incorporated.

(2) DU Control: All drive unit command and control functions areaccessed from this menu. First, the log in screen establishes useraccess and restrictions as well as confirms the correct drive unitidentification. Drive unit control functions include real time display,parameter table manipulation, system commands, and non-volatile memorycontrol.

(3) Setup: Includes real time display channel selection and sweep speed,communication port selection, as well as the user list update functions.

(4) Window: Standard Windows function which allows various open windowarrangement tools. Also, if windows overlap, the foreground window canbe selected from a list of open windows.

(5) Help: Standard Windows function that allows the user to search for afunction or command from an indexed list. Also, the program name,version number, and copyright notice are found under the “About WinMAV”selection.

The tool bar is a shortcut means of accessing various communication andcontrol functions.

These functions are summarized (from left to right) as follows:

(1) Open a real time data file for viewing. The graphical representationis similar to the actual file, showing an ECG and drive line pressurewaveform.

(2) Open an event log, or history record file. Depicted by a dinosaur.

(3) Print current data window. Icon depicts a printer.

(4) Previous screen. Stored file navigation tool, depicted by an arrowto the left.

(5) Next screen. Stored file navigation tool, depicted by an arrow tothe right.

(6) More data (zoom out). Depicted by a binoculars.

(7) More details (zoom in). Depicted by a magnifying glass.

(8) Make measurement. Depicted by a calipers.

(9) Initiate a partial cycle. Shows a partial cycle as seen in the realtime display waveform, and abbreviated by the letters PC.

(10) Begin real time data display. Shows a real time ECG waveform andthe abbreviation RT.

(11) Stop, or freeze real time display. Depicted by a snowflake.

(12) Begin recording data to disk. Depicted by a floppy disk icon.

(13) Stop recording data to disk. Depicted by a floppy disk icon with aline through the middle.

Several of the above buttons may be unavailable due to the current modeof the system. The unavailable functions are indicated graphically bymuting the color of the button. In other words, the button is “greyedout”. For example, prior to logging in to the system, only the open filefunctions are available.

In addition to the menu at the top of the screen, status informationappears at the top and bottom of each window. This is intended toprovide brief help information, or show additional data about aparticular file. The default message displayed at the bottom of thescreen is For Help, Press F1.

The status information is displayed based on the cursor position. Whenthe cursor is positioned over a particular tool bar button, a smalldescription of the button appears, if the mouse remains in thatposition. The information is in the form of a small window at thelocation of the cursor. Also, the status bar displays the sameinformation.

There are two types of files which may be saved during normal operationof WinMAV. These are: (1) real time data acquired by the drive unit andthe set of patient specific parameters, which sets a number of devicefunctions, and (2) the record of device history and error statistics.Regardless of specific file content, common rules govern file naming anddirectory location, as outlined below.

The drive unit serial number is extracted from the MachineIdentification Code and used as a directory name for all filesassociated with that particular unit. The directory itself is created byWinMAV at Log in time, but only if the user has Level 3 access (highestlevel). If no such directory is detected at run time, the applicationreports an error.

Data file names are generated automatically by the software, and eachname is unique and reflective of the data type. The name includes a timestamp, named for example in the format “yy_mm_dd _hh_mm_ss.drt” where“yy” is the year, “mm” is month, “dd” is day, “hh” is hour (24 hourformat), “mm” is minutes, and “ss” is seconds. The file extension is“drt”, which indicates this is a real time data file. The PatientParameter Table is automatically stored with the real time data, and isalways part of the real time display window. History record files usethe same file format, but with an “hst” file extension.

If the user wishes to add a new drive unit to the list without havingLevel 3 access, a directory may be created using standard Windows tools.For example, the Windows Explorer can create a new folder in the WinMAVroot directory (examples as follows);

L15 Line powered drive unit, serial number 15

W2 Wearable drive unit, serial number 2.

An error message is generated if there is a directory search failure.Each generated file is stored in the appropriate directory and bears aunique name, reflecting its data type.

The off line processing menu selections allow the operator to reviewpreviously recorded data. As noted in Log In, the user need not log into access stored files. Functions that are available are any of the Fileopen commands (event logs or real time data files), the Log In commandfrom the DU Control menu, and the Settings function from the Setup menu.

Much of the off line processing functions are similar to those under theStart Real Time menu. The functions launched during off line processingdiffer from those which are sub-functions of the Start Real Time menu inthe following ways:

(1) There is no channel selection on the stored file. If only twochannels were selected for recording, the third channel will not beavailable in the record.

(2) A seconds counter is displayed across the bottom of the firstchannel to allow the user to navigate very long records, or note whenevents occurred in a record.

(3) The addition of Previous Screen and Next Screen tool bar buttonsallow the operator to scan the record one frame at a time.

(4) The background is black (during real time measuring, the backgroundis blue).

Upon execution of an open command from the File menu or selection of ashortcut button from the tool bar, a window will pop-up that allows theuser to select a file with a default extension that matches the formatto be accessed. The standard Windows navigation tools are available tofind the desired file.

Once a file is opened, the real time display window shows the waveformsthat were selected by the Setup function. The patient parameter table isvisible on the right side of the real time window, and can be resized toshow more or less of the real time data. The background color of thedata window is black, to distinguish it from real-time data if multiplewindows are open. Real-time data windows use a dark blue backgroundcolor.

The tool bar buttons for data measurements are active as well as theMore Data and More Details functions. These features allow measurementsof time and amplitude on any stored real time waveform. Older files thatwere created by the DOS version of the program can be loaded into WinMAVand then saved in the new format. Comments may be added at any timeafter the files have been stored. The File:Save As menu function addsthe comments to the file.

In order to save the files for later storage, analysis, and retrievalfrom a database program, two File menu functions are implemented. Thefirst is DB Save RT Data, which saves the real time data file in aformat that can be recognized by the database. The second function is DBSave PPT, which performs the same function but strips the PatientParameter Table from the real time data.

Another database tool is the Copy Doc Path function from the File menu.This tool copies the DOS path and current temporal position of the datafile to the clipboard, which can be retrieved by the database forsimplified file pointers. For long real time data files, this allowsaccess to a particular point in time within any data record to be viewedby the database program.

The Log in Window requires three pieces of information. The OperatorInitials are used to keep a record of user modifications to theparameter table, as well as who recorded data to a particular file.Initials can be one to three characters in length, and are automaticallyconverted to capital letters. The second item is the unique userPassword, which consists of five to ten characters. The third item is acode which consists of the following information. Each drive unit has aunique Machine Identification Code hard coded into its memory, whichcorresponds to the drive unit serial number. All users are provided withthe scheme of the code naming which is a single continuous wordcontaining the general fields shown below:

<type> L for line powered, W for wearable

<id> Machine serial number

<secret> Code known only to users

Examples

L5<secret>—Line powered drive unit #5

W12<secret>—Wearable drive unit #12

No special access codes are required to view recorded data files. Thisis defined as Level 1 access.

The second layer of security (Level 2 access). requires all three piecesof information as described above. To this end, each user is given auser name (Physician Initials) and Password. The password is caseinsensitive.

As described previously, for Level 3 access, a special MachineIdentification Code allows access to functions designated for factoryauthorized users only. This is designed to protect the patient and thedrive unit from incorrect settings and avoid the loss of data.

Once the, Log In command is issued from the DU Control menu, the user isprompted with a pop-up log in screen. The <tab> key is used to cyclethrough the fields. Input from the keyboard is echoed in the fields,except that each Password entry and Machine ID appears as “*” forsecurity. A carriage return, or selection of the OK button completes thelog in operation, and the pop-up screen will close. Information isverified and either allow or deny access appropriately.

In the event the user inputs invalid information, the program reportsthe following error: “Incorrect log in data. Access denied!”. The userwill then be restricted to Level 1 access until correct data is input.

Similarly, if the Operator Initials and Password are input correctly butthe drive unit ID number is incorrect, a message will pop-up indicatingthe error as follows: “Incorrect drive unit ID. Please log in again.”This error will not be generated until the user attempts to communicatewith the drive unit.

Drive unit control menu contains all drive unit real time display andcontrol functions. One of these functions is the Start Real Time mode.The authorized user can view up to three channels of data from the driveunit. The possible channels are: (1) ECG, (2) MAV Drive Line Pressure,and (3) Differential Pressure. One purpose of the Real Time menus is toallow viewing of any combination of these signals at any time duringdrive unit operation. Gain, display sweep speed, and offset adjustmentsto the waveforms shown on the screen are available. In addition, signalsmay be recorded and stored to disk during the real time display of thedata.

The user can also freeze the display and perform timing and amplitudemeasurements on the desired waveform. Finally, the Read PPT menu optionsare available from the first level of the DU Control menu. This allowsthe operator to adjust patient parameters and see the effects of thesechanges without leaving the Real Time menu tree. However, the parametertable adjustments are available only when the display is frozen.

Once the data acquisition setup has been entered and the user hascorrectly logged in with Level 2 access, real time display can beinitiated. As stated in Start Real Time and shown in FIG. 8, there aretwo windows visible. One is the actual display of the selected channels,and the other is the Patient Parameter Table.

In addition to the real time data stream, the drive unit sends itsoperating, or machine state. The various machine states appear asdifferent colors on the displayed waveforms. A color scheme similar tothe one below is used:

Signal State Color ECG R-wave detected/absolute blanking light blue ECGT-wave (partial) blanking gray ECG Pacer spike red ECG Other (searchingfor R-wave) green MAV/Diff Filling time magenta MAV/Diff Deflation lightblue MAV/Diff Other gray BACKGROUND N.A. dark blue

The buttons available during real time display are as follows: MoreData; More Details; Stop/Freeze; and Start Recording. Buttons on thetool bar that are available after the screen is frozen: Open RT File;Open Event Log File; Print; Previous Screen; Next Screen; More Details;More Data; Measurements; Partial Cycle; and Start Real Time.

The Baseline is always visible in the real time window, regardless ofwhether the display is frozen or not. It consists of a horizontal linedrawn across the screen and corresponds to the baseline signal value,which is defined as (1) the average value of the signal in the case ofthe ECG, (2) atmospheric pressure in the case of the MAV drive linepressure, and (3) zero difference in the case of the differentialpressure sensor signal.

Activation of the Measurements button, in addition to the appearance ofthe cursors, causes a small text box to appear within the data viewingwindow.

Three values of interest appear in the text box:

(a) abbreviation for “absolute”, represents the value of the signalwhere it intersects the last moved cursor and the baseline value.

(d) the “difference” in amplitude values of the signals at the cursorintersection points.

(t) the amount of “time” elapsed between the vertical cursors.

The up and down arrows at the top of the box allow adjustment of theposition and size of the waveform. Specifically, the left set of arrowsadjusts the offset, while the right set of arrows adjusts the gain. Eachclick of the mouse on the arrow will incrementally increase or decreasethe offset or gain.

The Start Recording button will begin saving the raw data to the realtime data file given the naming protocol described in File Naming.During recording of the signal(s), the screen continues to scroll anddisplay the signals as they were in the Real Time:View screen. It shouldbe noted, however, that the data will be saved just as it was sent. fromthe drive unit, without any gain or offset adjustment. During therecording process, the only buttons available are Stop Recording andStop/Freeze.

The Stop Recording command automatically labels the record with defaultcomments that include the Operator Initials and Drive Unit ID, forsorting during playback. Also, the comments that are present in thecomments portion of the tool bar are saved to disk.

Also included in the file of real time data is the patient parametertable. The purpose of recording this information, is to allow retrievaland display of pumping parameters along side the real time data.

Each real time record that is saved to disk has a header that is uniqueto a type of drive unit (either WDU or LPDU).

The purpose of partial cycle function is to allow the user to determineif the machine settings are correct for detection of the dicrotic notch.There are two methods for performing a partial cycle. The user caneither choose Partial Cycle from the DU Control menu, or select the PCbutton from the tool bar. In either case, the machine enters a statewhere the real time display will continue for the current display sweeponly. Then the display will freeze and perform a number of calculations.

One of the most important concepts for setting up the drive unit timingis the concept of the “window” for detecting the dicrotic notch. Thesimplest explanation is that the window is the most likely time that thedicrotic notch is to occur after the detected R-wave. It should be wideenough to encompass any expected heart rate for the patient in question,barring any problems such as artifacts which may cause false detections.

After the screen is frozen and the detected notch is shown on thedisplay, it is then up to the user to determine if the drive unit hascorrectly detected the dicrotic notch. If it is correct and the windowfor detection is reasonable, no action is required, except perhaps tosave the record for future analysis. If the drive unit has incorrectlyfound the notch, the user must take further actions to ensure correctdrive unit operation.

A reasonable window for detection must be defined on a patient topatient basis with the authorization of a physician. Even if the windowis appropriate given the current patient status, if conditions changedramatically the settings may be inappropriate.

When the user activates the calculations function, a command is sent tothe drive unit to perform a timing update. After the partial cycle iscomplete and the display is frozen, the PC performs the followingfunctions:

(1) Calculate the mean, systolic, and diastolic patient pressures anddisplay the result at the bottom of the screen.

(2) Show where the computer found the dicrotic notch using the cursors,and display the time from the ECG to the notch in milliseconds.

(3) Show the method the computer used to find the notch (either fastestslope, actual notch, or nothing found—default).

(4) Display a colored bar at the top of the drive line pressure waveformwhich indicates the current “window” for detection of the dicroticnotch. This window consists of the dicrotic notch earliest, latest anddefault settings.

(5) Finally, the user may obtain a suggested set of settings for thedicrotic notch detection window.

In an example of the partial cycle measurement, if there is no ejection,the status bar at the bottom of the screen indicates this with the(Default) text. The first cursor shows the point of detection of theR-wave. The second cursor shows where the dicrotic notch was found, orif not found, the default setting. At the top of the second traceoverlapping the second cursor, is a small horizontal bar. This barindicates the “window” for dicrotic notch detection, which includes theparameter table settings as described above.

To continue real time display, the user must either select the RT buttonfrom the tool bar, or select Start Real Time from the DU Control menu.

The user should not select the freeze button during the partial cyclesweep. This action will stop the calculations and halt the real timetrace.

The authorized operator can access, retrieve, and update the patientparameter table. The parameters in the table are used by the drive unitto determine conditions such as an arrhythmia or deviation from normalsinus rhythm as well as to set operating parameters such as filling timeof the blood pump. The actual adjustments are made via WinMAV by anoperator authorized as described in Log In.

When the Read PPT button is executed from the Du Control menu, thesoftware will. issue a command to the drive unit to send the table.After receiving the patient parameter table, the module will save thetable values locally and display them.

Modification of parameters is done by double-clicking on the desiredparameter, and adjusting the slider control or entering values directly.The default value is shown in square brackets, and always visible in theleft corner of the slider bar window. Clicking on the OK buttoncompletes the adjustment of the local parameter table. Note that thedrive unit has not yet received the updated values.

The second method of changing parameter table values is from within thereal time display window, but only when the sweep is frozen. The methodis the same as discussed above.

After all desired parameters have been updated, the Update PPT selectionfrom the DU Control menu sends the data to the drive unit. The driveunit will receive the data and perform a CRC. If every check schemeverifies data integrity, the patient parameter table is be updated.

A simplified means of changing the dicrotic notch window settings(dicrotic notch earliest, latest, and default) is available. The methodsuggests a window for detection that is ±30% from the detected dicroticnotch. The default setting is equal to the detected dicrotic notch plus50 ms. The feature is activated by clicking the right mouse button inthe real time window after the Partial Cycle command has been executed.A confirmation window will pop-up asking if the user wishes to acceptthese settings. Selecting Yes will write the suggested values into theparameter table, but will not update the drive unit. The user shouldverify that the notch has been detected properly before accepting thevalues. After the drive unit operating parameters have been updated, thenext Scheduled Pressure Measurement uses the new window when searchingfor the dicrotic notch. The final action is to send the parameter tablewith the updated values by selecting the Update PPT function from the DUControl menu.

As an additional safety feature, the allowable limits for each editedparameter are displayed. Any value entered which exceeds or falls belowthe specified limits will be ignored. It will thereby be impossible forany operator to modify a parameter to a value outside of thepre-determined safety zone.

If the user attempts to close the parameter table window after changingvalues and has not sent the values to the drive unit, a window shallpop-up as a reminder to send the data to the drive unit. The user hasthe option to ignore the changes, or send the table.

In order to obtain an on-line description of each parameter tablesetting, the user can consult the help menu. The help windows reflectthe brief descriptions below.

(1) Scheduled Pressure Measurement. This refers to the amount of timebetween partial cycles for MAV drive line analysis.

(2) NSR Deviation. This parameter sets the % deviation allowed betweenthe last average R—R interval and that measured during the most recentpartial cycle, considered normal sinus rhythm (NSR).

(3) Pressure Measurement Lockout. A timing update can be the result ofNSR deviation. Frequent detection of this deviation would result infrequent partial cycle measurements. For patient safety, an absoluteminimum time between partial cycle measurements is set with thisparameter.

(4) Arrhythmia Threshold. An arrhythmia is diagnosed if the arrhythmiaindex described exceeds this threshold.

(5) Arrhythmia Inflate Delay. This parameter refers to the conservativesetting of the inflate command, which is set upon the detection of anarrhythmia.

(6) Dicrotic Notch Default. This parameter refers to the value used asthe dicrotic notch time if one is not found within the prescribed timeinterval.

(7) Dicrotic Notch Earliest. This parameter sets the time limit for theearliest detection of the dicrotic notch. Note that the table valuesshow an overlap of the earliest and latest settings for notch detection.The software will not allow the user to set these values incorrectly(i.e.: enter a value of 450 for Dicrotic Notch Earliest and 300 forDicrotic Notch Latest).

(8) Dicrotic Notch Latest. This parameter sets the time limit for thelatest detection of the dicrotic notch.

(9) Filling Time. This is the target value for the inflation duration.

(10) Inflation Adjustment. The “inflate valve open” command is set toprecede the dicrotic notch (t_(DN)) by a maximum of N msec to allow formechanical delays in the system. The Inflation Adjustment (IA) parameterdefines a delay such that inflation begins at a time equal to (IA−N)msec relative to t_(DN). The shortcut mode of adjustment is to use theReal Time plus and minus buttons in the adjustment window formodification of Inflation Adjustment and Deflation Adjustmentparameters. The appropriate parameter is changed in the parameter tableand the table is immediately sent, thereby updating the drive unitvalues. The user is not required to select the Update PPT button.

(11) Deflation Adjustment. The time between the R-wave trigger and thedeflation command is set by this parameter. The shortcut mode is thesame as in (10) above.

(12) Stroke Volume. This parameter sets the desired percent inflation ofthe blood pump. The calibration of the volume control algorithm is setat the factory.

(13) Assist Pressure Correction Factor. This is the value used toestimate aortic pressure at the end of inflation from values measuredduring a partial cycle.

(14) Pacemaker Blanking. The hardware detects the pacemaker pulse andsignals the processor via an interrupt line. R-wave blanking begins whenthis pulse is detected and extends for the period selected in theparameter table. While this blanking is in effect, the real time displaycolor is changed from. green to red.

If the above parameter is set to zero, a mode is entered that forces theR-wave detector to trigger only on the pacemaker pulse. This pulse isdetected in hardware and may not be visible on the display, but thesignal should turn from green to red as discussed previously.

When in pacemaker trigger mode, the parameter table will display a zerowith a series of exclamation points (O!!!!!) As a visual reminder thatthis mode is in effect.

TABLE 2 Range of Acceptable Patient Parameter Values Parameter UnitsMinimum Default Maximum Scheduled Pressure min 3 10 20 Measurement NSRDeviation % 10 20 80 Pressure Measurement sec 15 30 60 Lock-OutArrhythmia Threshold % 0 10 15 Arrhythmia Inflate Delay msec¹ 250 400500 Dicrotic Notch Default msec DNE entry 300 DNL entry Dicrotic NotchEarliest msec 150 180 450 (DNE) Dicrotic Notch Latest (DNL) msec 300 350552 Filling Time msec 60 96/128² 160 Inflation Adjustment msec −80 28 50Deflation Adjustment msec 0 0 152 Stroke Volume % 25 100 110 AssistPressure Correction mm Hg −20 0 50 Factor Pacemaker Blanking msec 12 2080 Pacemaker Trigger mode 0 N/A N/A ¹The millisecond values in the tableare stated as round numbers, however the program only has 4 millisecondresolution. Therefore, the listed value is only an approximation. Theactual value will be rounded to the nearest multiple of 4 milliseconds.²The WDU default filling time is 96 ms, while the LPDU default settingis 128 ms. These values have been chosen to maximize augmentation whileminimizing oscillations in the compressor speed control servo.

The drive unit software continuously updates a snapshot of the currentmachine state. Memory is allocated for a minimum of 20 possible“detected event” snapshots and a minimum of 21 or 28 event counters forthe wearable and line-powered units, respectively. Due to memorylimitations, the state of the machine is stored only at the time of theinitial occurrence of an event. Detailed records of subsequent eventsare not stored; however, the number of times each event occurs isrecorded.

Thus, at any given time, the drive unit memory contains (1) the currentoperating snapshot, (2) the collection of snapshots, and (3) eventcounters for each error condition. Items (2) and (3) constitute thehistory record or Event Log of the device.

When Event Log is selected from the DU Control menu, a window appearsthat shows all recorded events for that particular drive unit. Thewindow displayed contains three sub-sections. The first, leftmostsection includes the numbers of the available snapshots. The OP labeledsnapshot is for the operating snapshot (may or may not be generated byan error). The second section includes the snapshot data for theselected snapshot from section one. Finally, the third section containsthe statistical data for each error. The user simply selects thesnapshot to be viewed, and the appropriate data is displayed. The linelabeled Error Code that is present in the snapshot section ishighlighted along with the error statistic in the third section.

When an error is detected and the Event Log is downloaded, the firstsnapshot is highlighted by default. However, this is not the currenterror that was just detected. In order to determine the most recenterror, the user must select the operating snapshot to see the eventdata. A means of verifying that this is the correct error is to checkthe date and, time stamp of the error.

In order to save the Event Log data to disk, choose the Save As commandfrom the File menu. This command generates an automatically and uniquelynamed file which stores the entire history record and the operatingsnapshot.

The information stored in the event log is as follows:

(1) Event Code. Each type of flagged event will have a correspondingevent code.

(2) Time Stamp. Time elapsed since last power-up will be recorded.

(3) Working Time. The amount time mechanical parts have been inoperation since the unit left the factory will be recorded.

(4) Dicrotic Notch Time. The time of the “found” dicrotic notch will berecorded along with an indicator of which criterion was met (slopechange versus maximum slope).

(5) R-wave Detection Thresholds. These entries include both the currentslope and amplitude thresholds.

(6) Arrhythmia Quotient. This parameter is the current value of thearrhythmia detection quotient.

(7) NSR deviation. This value refers to the current difference betweenthe last average R—R interval and that measured during the most recentpartial cycle.

(8) Filling Time. The most current value of the inflation duration (ID)variable and target ID will be recorded.

(9) Motor Speed Parameter. The current % modulation or duty cycle willbe recorded.

(10) Integration Sums. These values refer to the current value andtarget value of the accumulated ΔP summation used for volumedetermination.

(11) Pressure Gradient. This is the current estimate of the differencebetween the MAV drive line pressure and the aortic pressure at the endof inflation.

(12) Reservoir Pressures. The maximum and minimum pressure of eachreservoir (during the last cycle) will be recorded (the Wearable DriveUnit has only 1 reservoir).

(13) Partial Cycle Time. This refers to the amount of time expired sincethe last partial cycle and MAV drive line waveform analysis.

(14) Patient Conditions. The patient parameters determined from the mostrecent drive line analysis will be recorded. These include: (i) meanaortic blood pressure, (ii) systolic peak pressure, (iii) blood pressureat the dicrotic notch, (iv) the minimum aortic pressure, and (v) theaverage R—R interval.

The only states that are displayed in the event of an error are theactual error condition or machine state. In the case where an error hasnot occurred or the state has not been defined or initialized yet, thestate or error shall read N/A. Other parameters shall denote a lack ofinformation via the words “Unknown”, “No Data”, or with zeroes in thecase of undefined numerical readings.

Self test modules are performed prior to pumping, and an error conditionis produced if any test condition is not satisfied. In addition to thesespecific device function tests, a number of operating conditions will beevaluated throughout normal operation. In the event of any error (selftest or operational), an alarm will sound (beep), an LED will be lit,and an action will be taken. There are 3 LED indicators on the unitwhich correspond to different types of errors: (1) Battery Status(yellow), (2) Connection Error (red), and (3) System Error (red).

In addition, the battery status LED will flash (0.5 Hz) in the event ofa low battery condition. The detection of most errors will effect apower down sequence, which turns the motor off and enters a defaultvalve state, which results in deflation of the blood pump. All detectederrors will be recorded in the error log. The following items describesome of the more common error conditions and system responses which mayoccur during normal operation.

(1) Line Power Disconnected: If the line power is disconnected from thedrive unit, the hardware automatically switches to battery operation andsignals the processor. The patient/operator will be alerted any time thepower supply switches over to battery operation. The Caution alarm willsound twice (10.5 seconds total) and the Battery Status LED will flashfor 10 seconds.

(2) Battery Capacity/Status (Error 02): The battery status is monitoredthroughout normal operation. The voltage is monitored once everyacquisition cycle (every 4 ms). A level below a predetermined valueconstitutes a “low battery” condition. A level below a second (lower)predetermined value constitutes a “discharged battery” condition. Thelow battery condition will cause the Battery Status LED to flash and theCaution alarm to sound. Under the discharged battery condition, theBattery Status LED will be activated continuously, the Warning alarmwill sound, and the unit will be powered down.

(3) Detached Drive Line (Error 03): A disconnected drive line willprohibit operation of the pump. The error condition will result in theactivation of the Connection Error LED, the Warning alarm will sound,and the unit will be placed in the power down state.

(4) Temperature Shut Down (Error 04): Component operation causes someheating within the unit housing during normal pumping. Excessive heat orcold may cause unreliable operation. If a temperature outside of theoperating range is detected, the System Error LED will be activated, theWarning alarm will sound, and the unit will be powered down.

(5) Pressure Reservoir Pressure Out of Range (Error 14 (low) and 15(high)): During normal operation, the pressure reservoir tank is beingpressurized at all times except inflation. Although the safety reliefvalve will be checked during the self-test, its operation will beensured by continuous monitoring. In addition, an “insufficientpressure” condition would indicate possible valve leakage or inadequatecompressor function. If the reservoir pressure falls outside of itsexpected range, an error will result. The System Error LED will beactivated, the Warning alarm will sound, and the unit will be powereddown.

(6) Vacuum Reservoir Pressure Out of Range (LPDU only, Error 26 (high)27 (low)): The vacuum reservoir tank is being evacuated at all timesexcept deflation. As with the pressure reservoir, the relief valve willbe checked during the self-test and its operation will be ensured bycontinuous monitoring during normal pumping. An “insufficient vacuum”condition would also indicate possible valve leakage or inadequatecompressor function. An error will result if the reservoir pressurefalls outside of its expected range. The System Error LED will beactivated, the Warning alarm will sound, and the unit will be powereddown.

(7) R-wave Lost (Error 16): Correct detection of the ECG R-wave iscritical for the proper triggering and pumping sequence. A loss ofR-wave detection is likely to be a connection error. If such a lossoccurs, the Connection Error LED will be activated, the Caution alarmwill sound, and the unit will be powered down.

(8) High Pressure in MAV Drive Line (Error 17): Pressure in the MAVdrive line which exceeds a certain limit is a more serious conditionthan an insufficient pressure scenario. The Connection Error LED will beactivated, the Warning alarm will sound, and the unit will be powereddown.

(9) High Pressure Gradient Across Blood Pump Membrane (Error 18):

Repeated exposure to large pressure gradients across the blood pumpmembrane could result in premature fatigue. Since MAV assisted aorticpressure cannot be monitored during pumping, this pressure gradientcannot be measured directly during normal operation; however, it can beestimated as follows: The estimation scheme relies on the assumptionthat relative difference between MAV assisted aortic pressure and aorticpressure during systole remains constant. Prior to the patient'stransfer from ICU, arterial pressure is clinically monitored such thatsystolic pressure (P_(systole)) and MAV assisted aortic pressure(P_(assisted)) are determined simultaneously. By defining an offset orcorrection factor (CF) as the difference between these(P_(assisted)−P_(systole)), the MAV assisted aortic pressure can besubsequently estimated if systolic pressure is known. (Note: If thesystolic pressure and the MAV assisted pressure are equal, thecorrection factor is zero.) During normal operation of the drive unit,the systolic pressure measured during a partial cycle and CF (stored inthe patient parameter table) can be used to estimate MAV assisted aorticpressure (_(Passisted)=_(Psystele)+CF). Further, the differentialpressure across the MAV membrane can be estimated during normaloperation as the difference between this value and the MAV drive linepressure (P_(MAV)) If the differential pressure exceeds a prescribedlevel, the System Error LED will be activated, the Warning alarm willsound, and the unit will be powered down.

(10) Blood Pump Pressure Rise While Inflated (Error 18): Pressure risein the blood pump after the common valve is closed could be indicativeof a valve leak. The Connection Error LED will be activated, the Warningalarm will sound, and the unit will be powered down.

(11) Incomplete Deflation (Error 20): Incomplete blood pump deflation isa serious potential error and could indicate a Common valve failure.Upon detection of this error, the unit will be powered down. The SystemError LED will then be activated, and the Warning alarm will sound.

(12) Watchdog Shut Down (Error 22): Failure of the watchdog serviceroutine to address the watchdog timer under normal operating conditionsis an indication that the CPU has been rendered inoperative. Such anundefined failure cannot be tolerated. In this case, the System ErrorLED will be activated, the Warning alarm will sound, and the unit willbe shut down.

(13) Leak Detection (LPDU only, Error 28): The isolation chamber/driveline/blood pump system should maintain a fixed amount of air duringnormal operation. Incomplete blood pump deflation can be caused by airleaking into the system. Incomplete inflation or excessive vacuum duringdeflation could result from air leaking out of the system.

By comparing beat-to-beat deflation pre-charge pressures to thatmeasured during the most recent Fill cycle, possible leaks can bedetected. Upon detection of a leak, the unit will be powered down. TheSystem Error LED will then be activated, and the Warning alarm willsound.

During normal operating mode or factory updates, the operator may wishto perform several functions which directly control the device. Thismode allows the physician or other authorized operator to executeoperating commands to the drive unit. Examples of control commands arethe ability to start and stop pumping, or initiate a partial cycle.

If the operator has appropriately and correctly logged in, devicecommands are available from the menu. In the DU Control menu, there areseveral commands that control the drive unit directly, or change thestored statistics.

Reset DU: Activation of this button is restricted to Level 3 access(factory personnel only) via the special user Machine IdentificationCode. The button is used to reset the drive unit memory.

This command reinitializes all buffers and variables as if the devicehad never been powered-up. That is, the device memory is reset to itsfactory values. When this command is issued, the WinMAV softwareautomatically saves the event log to disk, following the prescribed filenaming convention.

Reset Event Log: In this case, the History Record and event statisticsare reset. As noted in Event Log, the memory allocated for the wearableand line-powered units, respectively, contain a minimum of 20 possible“detected event” snapshots and a minimum of 21 or 28 event counters.That is, the memory limitations of the drive units necessitate that thestate of the machines be stored only at the time of the 20 initialoccurrence of these events and that subsequent events are merelyregistered as “counts”. As with the above command, the WinMAV softwareautomatically saves the event log to disk.

Stop Pumping/Resume Pumping: The operator may wish to evaluate thepatient's condition with assistance versus without assistance. Thesemenu buttons serve to directly control the pumping action of the driveunit.

Timing Update: Activation of this command from the DU Control menu,results in the drive line waveform analysis actions and updatesdescribed in the user documentation for each drive unit. Brieflysummarized, the drive line analysis will result primarily in an updateof the dicrotic notch time and therefore, the inflation command time. Inaddition, this analysis generates an update record of the most recentlydetermined values of peak systolic pressure, diastolic pressure, meanpressure, and time from the R-wave to the dicrotic notch.

It should be noted that this command does not act the same way as thePartial Cycle command. Although the drive unit performs the same action,the WinMAV program does not freeze the display with cursor indicators,or calculate any patient pressures.

Therefore, there is no feedback as to where the dicrotic notch wasdetected.

Snapshot: As noted in Event Log, the software of the drive unitcontinuously updates a snapshot of the machine state. In contrast to theEvent Log command, as issued from the DU Control menu, this operatingsnapshot opens a window and provides a button for a New Snapshot. Inthis way, the user can get several snapshots in succession without goingthrough the normal menu structure.

In addition to the normal functions of the patient parameter table, acalibration mode may be entered. As discussed in Data Security andIntegrity Requirements, the factory authorized user with Level 3accessmay adjust the definition of 100% stroke volume. If the desired volumeis 50 cc (for example), the user may input an adjustment value whichincreases the output to 50 cc for a setting of 100% .

After the stroke volume calibration is complete, when the parametertable is read the user will not see evidence of the calibration. Thisinformation is transparent to the user, and cannot be modified withoutentering the password specific to this mode.

The first action required is to access the patient parameter tableeither from the Start Real Time function or the Read PPT function. Thenthe authorized user can calibrate the system by selecting the StrokeCalibration setting from the DU Control menu. This action brings up aslider window that allows input of values as shown below:

Min: 80% Default: 100% Max: 140%

Once the desired setting has been entered, the user must select the OKbutton to send the information to the drive unit. In this case, the useris not required to send the data to the drive unit with the Update PPTfunction. After correct transmission, the communication softwareresponds with a message as follows: “Stroke volume correction wassuccessfully completed!”

Values outside this range are not accepted by the WinMAV software andwill bring up an error message warning that the setting exceeds thelimits.

At the Settings function of the Setup menu, channel selection, sweepspeed, and serial communication port settings are input. The buttonsallow selection of ECG/MAV/Diff/None to select the signal(s) to beretrieved from the drive unit and displayed in one or more of thesubsequent display windows.

Given the menu selections as described above, the user can select thedata display properties for real time waveforms. That is, the data sentto a file reflects the same number of channels as the real time displaywindow. Three channels maximum are available for viewing in any order.

The user may also select the sweep speed via a slider bar withadjustment between Detailed and Epoch. The range of speeds isapproximately from one to ten seconds (epoch), with discrete settings inbetween.

Finally, the user must select the port set up for RS-232 serialcommunication on the personal computer. On most laptop computers, thiswill be COM1.

If the wrong port is selected, the WinMAV software responds with a Noresponse from drive unit error message.

The security protocols require the use of a password for access toWinMAV functions that allow modifications to drive unit operation. Inorder to enable various users to access the system, a user list has beendevised to describe all authorized personnel allowed to access the driveunit. The list contains all user initials and passwords, and isencrypted for security.

The factory authorized user who wishes to update the list of users forthe MAV system may do so with one security code. This code is entered byselecting the User List function from the Setup menu. At this time, awindow will pop-up asking for the password. The password is echoed inthe widow with the “*” character as it is entered.

Successful entry will bring up a window that includes all authorizedusers and their password.

The actual list is updated as a simple text file, with standard editingfunctions available. Each line in the list consists of an entry thatincludes the initials and the password, separated by one or more spaces.

After the list has been updated, the user should click on the OK buttonto encrypt the file and store it to disk.

ANIMAL TEST EXAMPLE

This example will discuss the method for logging in, evaluating patienttiming, setting up the parameter table, and evaluating drive unitperformance. The goal is to maximize the drive unit effectiveness, whichwill in turn provide the maximum patient benefit.

Execute the program by double clicking on the icon on the desktop aswith other standard windows applications. The program will start up withmost buttons greyed-out. The first action is to select the Log infunction from the DU Control menu. Enter the user name, password, anddrive unit ID as discussed in Log In. All necessary functions should nowbe available.

Prior to activation of the drive unit, the user should evaluate thepatient to determine the general timing from the R-wave to the dicroticnotch (or Q-S₂) in milliseconds. This can be done via a number oftechniques, which will not be discussed in this document. If aperipheral blood pressure is used to determine timing, this pressure isdelayed in time by an unknown number of milliseconds. This must beconsidered when using this pressure for setting up the timing. Assumingthat the Q-S₂ value is known, this number can be used to select thewindow for dicrotic notch detection.

At this time, the drive unit can be activated by pressing the PumpOn/Off switch. If this is the first time the system has been activatedon the patient (in the O.R. for example) the user should immediately goto the DU Control menu and select Stop Pumping. This allows the user toverify correct ECG triggering prior to activating the pump. Pumping mustalways be synchronous to the heart immediately after the pump has beenimplanted to minimize the stress on the suture lines. Assuming that thetrigger is valid, as shown by the color changes in the waveform, theuser can now set up the pump timing.

The window for dicrotic notch detection should be set given the patientevaluation completed earlier. Assuming that the heart rate has notchanged drastically, go to the Read PPT selection from the DU Controlmenu. The resulting pop-up window reflects the current settings in thedrive unit. Set the dicrotic notch earliest, latest and default settingsas described in Patient Parameter Table. The default value should beabout 50 ms later than the current dicrotic notch. Select Update PPTfrom DU Control when complete. This sends the updated values to thedrive unit. If the heart rate has changed since the previous evaluation,the patient evaluation procedure should be repeated. This will ensurethat the pump will start with the best possible settings for the currentheart rate. The other parameter table values should be evaluated forcorrectness for the given patient.

Now that the ECG is valid and the pump timing has been adjusted, go tothe Resume Pumping selection of the DU Control menu. The drive unitshould begin the pump sequence, perform a partial cycle, and pumpaccording to the detected dicrotic notch. The user can evaluate notchdetection by selecting the PC or partial cycle button from the tool bar.The drive unit will perform the cycle and complete the calculations. Ifthe notch was detected properly and the window is adequate for arelatively wide range of heart rates, the system is set up correctly andperforming to specifications. The user should add appropriate commentsand save the partial cycle window to the hard disk with the Save Ascommand from the File menu. Normally, the stop pumping and start pumpingfunctions are not necessary. This is only important if there is aquestion of the ECG trigger or dicrotic notch settings. Upon performinga partial cycle, the “suggested settings” method can be used to updatethe patient parameter table, as discussed in Patient Parameter Table.

Drive unit operation should be evaluated on a regular basis using theWinMAV software as a tool. Periodically perform a partial cycle andverify that the dicrotic notch is detected properly and the window fordetection is adequate.

EXAMPLE WAVEFORM

In an example of a partial cycle where the dicrotic notch was detectedin the animal model,-the window for detection is very wide (as shown bythe bar on the second trace), allowing for dicrotic notch detectionunder a Wide range of heart rates. However, this wide a range can alsocause problems if noise or artifacts causes a false detection.

This is where the physician must make a decision. When there is noproblem detecting the notch given a wide window for detection, this isthe best scenario. If detection problems arise, the window should beadjusted to avoid false detections. This may be achieved by limiting thewindow to a narrower range, forcing detection in this zone. Also noticethat the default setting for the notch is slightly later than the actualdetected notch. This is a conservative approach that errs on the side ofsafety. That is, it is better to inflate late rather than early if thenotch is not detected.

The entire disclosure of the prior provisional patent applicationsSerial No. 60/060,499 filed Sep. 30, 1997, and Ser. No. 60/097,819 filedAug. 25, 1998 are considered a part of the disclosure of theaccompanying application and are hereby incorporated by reference.Additional information regarding the percutaneous access device can beobtained from U.S. Pat. No. 4,634,422 issued Jan. 6, 1987; U.S. Pat. No.5,242,415 issued Sep. 7, 1993; U.S. Pat. No. 4,913,700 issued Apr. 3,1990; and U.S. Pat. No. 5,833,655 issued Nov. 11, 1998 for apercutaneous access device having a removable turret assembly and areincorporated by reference herein. Additional information regarding theblood pump can be obtained from U.S. Pat. No. 4,630,597 issued Dec. 23,1986 which is incorporated by reference herein. Additional informationregarding the pressure control system and partial cycle blood pressuresensing can be obtained from U.S. Pat. No. 6,042,532 issued Mar. 28,2000 and U.S. Pat. No. 5,833,619 issued Nov. 10, 1998 which areincorporated by reference herein.

Referring now to FIG. 9, a graph illustrates an electrocardiogram signal90 with respect to time in the upper portion, and a pressure cycle ofthe pump according to the present invention including a pressure cycleshown in solid line 92 in the lower portion of the graph. For comparisonpurposes, aortic pressure line 94 is superimposed over the lower portionof the graph to illustrate aortic pressure of a patient during ascheduled pressure measurement procedure as disclosed in U.S. Pat. No.5,833,619, which is incorporated herein by reference in its entirety.Starting at the left, the aortic pressure receives full assistanceduring the deflation portion of the cycle as indicated by the uppernumeral 1 with a downwardly pointing arrow adjacent that portion of theaortic pressure line 94. The pressure measurement routine is thenstarted by partially inflating the inflatable chamber providing onlypartial assistance to the aortic pressure of the patient as indicated bythe upper numeral {fraction (1/2)} adjacent the upwardly pointing arrowduring the partial inflation procedure of the aortic pressure line 94.The inflatable chamber is maintained in a flaccid partially inflatedstate to obtain the aortic pressure wave form providing no assistance asindicated by the upper numerals 0 adjacent the upwardly directed arrowand downwardly directed arrow of these portions of the aortic pressureline 94. The zero numeral indicates that no assistance is given to thecardiac function during this portion of the cycle. At the end of thepressure measurement cycle, the inflatable chamber is deflated providingpartial assistance to the cardiac function as indicated by the uppernumeral {fraction (1/2)} adjacent the downwardly extending arrow of theaortic pressure wave line 94. In contrast, the aortic pressure wave formaccording to the present invention is illustrated in the pressure waveline 96. Beginning at the left side of the graph, cardiac function isassisted with deflation of the inflation chamber as indicated by thelower numeral 1 adjacent the lower downwardly extending arrow, thisportion of the wave form is identical to that provided in the pressurewave form line 94. The pressure measurement procedure for monitoring thepatient is then initiated. In the present invention, the inflatablechamber is inflated in the same manner as a normal cycle providing fullassistance to the cardiac function as indicated by the lower numeral 1adjacent the upwardly extending arrow, as compared to the partialassistance provided during partial inflation of the inflatable chamberassociated with the aortic pressure wave line 94. This raises the aorticpressure wave line 96 according to the present invention above the waveline 94 in this region. According to the present invention, theinflatable chamber is partially deflated to provide a flaccid, partiallydeflated chamber for measuring the aortic pressure wave form of thepatient. The partial deflation of the chamber provides cardiacassistance to the patient as indicated by the lower numeral {fraction(1/2)} adjacent the lower downwardly extending arrow associated with thewave line 96, as compared with the wave line 94 which provides noassistance to the aortic pressure of the patient during this portion ofthe cardiac function. The flaccid, partially filled inflatable chamberis then used to obtain the aortic pressure wave form during the patientmonitoring procedure and no assistance to the cardiac function isprovided during this portion of the cycle as indicated by the lowernumeral 0 adjacent the lower downwardly extending arrow associated withthe pressure wave line 96. At the end of the pressure measurementroutine, the inflatable chamber is deflated providing partial assistanceto the cardiac function as indicated by the lower numeral {fraction(1/2)} adjacent the lower downwardly extending arrow associated withwave line 96. By inflating the chamber and then partially deflating thechamber prior to the aortic pressure wave from measurement, the presentinvention provides additional assistance to the cardiac function of thepatient. This can have two benefits. First, the present invention canreduce the deflation adjustment factor criticality by obtaining moreaccurate partially assisted dicrotic notch measurement, and second thepresent invention increases partial assistance to the patient, so thatmeasurements can be taken on a more frequent basis without adverselyaffecting the patient. The previous pressure measurement procedureprovided only minimal assistance during two complete cycles of cardiacfunction, while the present invention provides improved assistanceduring the pressure wave form measurement procedure.

Referring now to FIG. 10, a simplified flow chart illustrates controlprogram steps to partially deflate the cardiac assist device during apressure measurement procedure. Step 100 initializes the partialdeflation routine of the program to partially deflate the cardiacassistance device to a predetermined volume. The steps typically includesetting memory storage registers to zero, and other values to respectivedefault settings. The inflation valve has previously been closed, andthe deflation valve is opened to begin deflating the inflatable chamber.During deflation, the deflation valve functions as a metering orifice.Step 102 measures a differential pressure between an upstream pressuresensor and a downstream pressure sensor. The differential pressure isaccumulated over time in a memory register at step 110. Step 110accumulates the differential pressure measurement corresponding to theaccumulated incremental volume to the contents of the memory register.The memory register is then evaluated to determine whether theaccumulated differential pressure measurements determine whether theaccumulated differential pressure measurements are greater than apredetermined value in step 114. If the memory register is not greaterthan the predetermined value, the routine returns to step 102. If thememory register is greater than the predetermined value, then theinflatable chamber is sufficiently, partially deflated in order tocontinue the scheduled patient monitoring pressure measurementprocedure.

Within the environment of the patient, the fluid pressure in thepartially deflated, flaccid pump correspondingly mirrors the arterialpressure. After the pump is partially deflated, the pump is allowed tosettle while the valves are closed to isolate the chamber from the drivemeans corresponding to step 116. Settling equalizes pressures throughoutthe isolated inflatable chamber and on either side of the membrane ofthe pump, allowing the isolated inflation chamber to act as a pressuretransducer. A pressure sensor measures pressure within the partiallydeflated, inflatable chamber of the pump corresponding to the arterialpressure of the patient. The controller obtains the aortic pressure waveform based on the pressure measurements readings taken approximatelyevery four milliseconds, for at least one cardiac cycle during thescheduled patient monitoring pressure measurement procedurecorresponding to step 118.

Based on the stored information of the cardiac cycle, taken during thescheduled patient monitoring pressure measurement procedure, thedicrotic notch can be detected from a reverse slope occurring within aphysician adjusted time window. If not found, detection of negative tozero slope is checked, or if that is not found, detection of the largestnegative slope of a minimum duration is checked. If no notch is detectedwithin the time window, the dicrotic notch default specified in apatient parameter table stored in the controller is used. The controlleralso monitors the QRS complex from the ECG signal taken during thescheduled pressure measurement procedure. From this stored information,the controller computes the time from the QRS complex or R wave to thedicrotic notch as the systolic time interval. As a result, pumpingbegins with up-to-date patient information. The detection of the eventscan be adjusted or overridden by a physician within safety parameterwindows, if the patient has special needs. These parameters are storedin the non-volatile memory of the controller. Pumping continues with thedefined parameters until another timing update is mandated. Thescheduled pressure measurement is executed at a time interval typicallyranging from three to twenty minutes. The scheduled pressure measurementprocedure can be requested ahead of schedule, if the heart rate changesby more than 20% or other physician programmable change of between 10%to 80%.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiments but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, which scope is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures as is permitted under the law.

What is claimed is:
 1. A method for assisting cardiac function during acardiac cycle of a patient having a cardiac assist device with aninflatable chamber operatively disposed with respect to an aorta of thepatient comprising the steps of: cyclically inflating and deflating theinflatable chamber with a pressurized gaseous fluid synchronously with aheart beat of the patient based on a first set of programmable patientparameters relating to heart function; periodically conducting a patientmonitoring procedure, wherein the procedure includes the steps of:partially deflating the inflatable chamber to a predetermined volume ofpressurized gaseous fluid; isolating the inflatable chamber when theinflatable chamber is in a partially deflated, flaccid state andallowing the inflatable chamber to settle so that the inflatable chamberacts as a transducer; measuring a pressure waveform over time in theinflatable chamber with an external pressure sensor, wherein saidpressure in the inflatable chamber corresponds to current blood pressureof said patient when the inflatable chamber is in the partiallydeflated, flaccid state; monitoring pressure in the inflatable chamberfor at least a partial cardiac cycle; storing said monitored pressurevalues in memory of a controller; updating patient parameters based onsaid stored pressure values; and thereafter, cyclically inflating anddeflating the inflatable chamber with pressurized gaseous fluidaccording to the updated patient parameters until modified by anotherpatient monitoring procedure.
 2. The method of claim 1 wherein thepartial deflating step further comprises the steps of: expellingpressurized fluid from the inflatable chamber through a deflation valve;measuring a differential pressure across the deflation valve; andintegrating the differential pressure with respect to a time intervalcorresponding to an amount of time the deflation valve is in an openposition to determine a volume of fluid expelled from the inflatablechamber.
 3. The method of claim 1 wherein the conducting step isperformed at predetermined time intervals.
 4. The method of claim 1further comprising the steps of: monitoring a heart beat rate of thepatient; and performing the conducting step immediately, if a monitoredchange in heart beat rate of the patient exceeds a predeterminedpercentage.
 5. The method of claim 1 further comprising the step of:selectively scheduling the patient monitoring procedure for execution ata time interval ranging from three minutes to twenty minutes, inclusive.6. The method of claim 1 further comprising the step of: selectivelyscheduling a patient monitoring procedure, if a heart rate of thepatient changes by more than a preselected percentage value of anaverage of a predetermined number of previously measured heart ratevalues, the preselected percentage value selected in a range between 10%to 80%, inclusive.
 7. A program stored in memory for assisting cardiacfunction during a cardiac cycle of a patient having a cardiac assistdevice with drive unit connectible to an inflatable chamber operativelydisposed with respect to an aorta of the patient comprising the stepsof: automatically controlling the drive unit in response to aperiodically scheduled patient monitoring routine for measuring valuesof physiology of the patient; using measured values as modified inaccordance with physician programmable parameters for assisting cardiacfunction of the patient; interrupting counterpulsation for at least apartial cardiac cycle to perform the periodically scheduled patientmonitoring routine in order to obtain an aortic pressure waveformthrough a partially deflated, flaccid, inflatable chamber; and measuringa Q-S₂ interval by the control program from the aortic pressure waveformobtained.
 8. The program of claim 7 further comprising the step of:providing a patient parameter table having a plurality of physicianprogrammable parameters for modifying cardiac function assistanceprovided to the patient.
 9. The program of claim 7 wherein each of thephysician programmable parameters is restricted to a value greater thanor equal to a predefined minimum value and less than or equal to apredefined maximum value.
 10. The program of claim 7 wherein each of thephysician programmable parameters has a predefined default value. 11.The program of claim 7 further comprising the step of: adjustingsettings of the drive unit with a software program connectible inelectronic communication with the drive unit.
 12. The program of claim11 wherein the software program retrieves current values of physicianprogrammable parameters.
 13. The program of claim 11 wherein thesoftware program selectively retrieves a history of the drive unitoperation including error detection records.
 14. The program of claim 11wherein the software program displays a continuous ECG.
 15. The programof claim 11 wherein the software program displays a single-beat sampleof aortic pressure waveform obtained in real time from the patient. 16.The program of claim 7 further comprising the step of: using themeasured Q-S₂ interval to adjust inflation timing of the blood pump, asmodified in accordance with the physician programmable parameters, inresponse to changes in the heart rate and hemodynamic state of thepatient.
 17. A method for assisting cardiac function during a cardiaccycle of a patient having a cardiac assist device with an inflatablechamber operably disposed with respect to an aorta of the patientcomprising the steps of: partially deflating the inflatable chamber to apredetermined volume of fluid delivered from a source of pressurizedfluid, wherein the inflatable chamber is defined at least in part by aflexible membrane and the flexible membrane is flaccid when partiallydeflated to said predetermined volume of fluid; isolating the inflatablechamber when the flexible membrane is in a partially deflated, flaccidstate; and measuring a pressure waveform over time in the inflatablechamber with a pressure sensor located external with respect to thepatient, wherein pressure in the inflatable chamber corresponds to bloodpressure of the patient when the flexible membrane is in the partiallydeflated, flaccid state.
 18. The method of claim 17 further comprisingthe step of: storing the measured pressure wave form over time of theinflatable chamber for at least a partial cardiac cycle.
 19. The methodof claim 17 wherein the step of partially deflating the inflatablechamber further includes the step of: measuring a differential pressureacross an deflation valve disposed between the inflatable chamber and anexhaust port.
 20. The method of claim 19 wherein partially deflating theinflatable chamber further includes the steps of: accumulating thevolume expelled during each sampling time interval; and comparingaccumulated volume to a predetermined volume value.
 21. The method ofclaim 20 wherein partially deflating the inflatable chamber furtherincludes the step of: closing a deflation valve when the accumulatedvolume removed from the inflatable chamber is at least equal to saidpredetermined volume value.
 22. An apparatus for assisting cardiacfunction during a cardiac cycle of a patient having a cardiac assistdevice with an inflatable chamber operatively disposed with respect toan aorta of the patient comprising: means for partially deflating theinflatable chamber to a predetermined volume of fluid delivered from asource of pressurized fluid, wherein the inflatable chamber is definedat least in part by a flexible membrane and the flexible membrane isflaccid when partially deflated to said predetermined volume of fluid;means for isolating the inflatable chamber when the flexible membrane isin a partially deflated, flaccid state; and means for measuring apressure waveform over time in the inflatable chamber with a pressuresensor located external with respect to the patient, wherein pressure inthe inflatable chamber corresponds to blood pressure of the patient whenthe flexible membrane is in the partially deflated, flaccid state. 23.The apparatus of claim 22 further comprising: means for storing themeasured pressure wave form over time of the inflatable chamber for atleast a partial cardiac cycle.
 24. The apparatus of claim 22 furthercomprising: means for measuring a differential pressure across andeflation valve disposed between the inflatable chamber and an exhaustport.
 25. The apparatus of claim 24 wherein said means for measuringdifferential pressure across the deflation valve further comprises: afirst pressure sensor located upstream of the deflation valve; and asecond pressure sensor located downstream of the deflation valve. 26.The apparatus of claim 22 further comprising: a pressure reservoir forcontainment of a quantity of gas under pressure.
 27. The apparatus ofclaim 22 further comprising: drive means for cyclically controlling aninflation/deflation cycle of the inflatable chamber in response topatient parameters relating to heart function, said drive means havingat least one inflation valve, at least one deflation valve, and controlmeans for selectively opening and closing said valves.
 28. The apparatusof claim 23 further comprising: means for sensing a pressure waveformover time during the cardiac cycle of the patient comprising the stepsof: partially deflating the inflatable chamber to a predetermined volumeof pressurized fluid, wherein the inflatable chamber is defined at leastin part by a flexible membrane and the flexible membrane is flaccid whenpartially deflated with said predetermined volume of fluid; isolatingthe inflatable chamber when the flexible membrane is in a partiallydeflated, flaccid state; and measuring a pressure waveform over time inthe inflatable chamber with a pressure sensor located external withrespect to the patient, wherein pressure in the inflatable chambercorresponds to blood pressure of the patient when the flexible membraneis in the partially deflated, flaccid state.
 29. An apparatus forassisting cardiac function of a patient comprising: an inflatablechamber operably positionable with respect to an aorta of the patient; apercutaneous access device implantable with respect to a hypogastricregion of the patient and connectible in fluid communication with theinflatable chamber; and a drive unit connectible through thepercutaneous access device for selectively inflating and deflating theinflatable chamber in accordance with a control program stored inmemory, the control program for controlling the drive unit in responseto a periodically scheduled patient monitoring routine for measuringvalues of the physiology of the patient, and the control program usingmeasured values as modified in accordance with the control program andphysician programmable parameters for assisting cardiac function of thepatient, wherein the control program interrupts counterpulsation for atleast a partial cardiac cycle to perform a periodically scheduledpatient monitoring routine in order to obtain an aortic pressurewaveform through a partially deflated, flaccid, inflatable chamber, anda Q-S₂ interval is measured by the control program from the aorticpressure waveform obtained.
 30. The apparatus of claim 29 wherein thecontrol program further comprises: a patient parameter table havingphysician programmable parameters for modifying cardiac functionassistance provided to the patient.
 31. The apparatus of claim 29wherein each of the physician programmable parameters is restricted to avalue greater than or equal to a predefined minimum value and less thanor equal to a predefined maximum value.
 32. The apparatus of claim 29wherein each of the physician programmable parameters has a predefineddefault value.
 33. The apparatus of claim 29 further comprising: asoftware program connectible in electronic communication with thecontrol program for adjusting settings of the drive unit.
 34. Theapparatus of claim 33 wherein the software program retrieves currentvalues of physician programmable parameters.
 35. The apparatus of claim33 wherein the software program selectively retrieves a history of thedrive unit operation including error detection records.
 36. Theapparatus of claim 33 wherein the software program displays a continuousECG.
 37. The apparatus of claim 33 wherein the software program displaysa single-beat sample of aortic pressure waveform obtained in real timefrom the patient.
 38. The apparatus of claim 29 wherein the controlprogram uses the interval to adjust inflation timing of the blood pump,as modified in accordance with the physician programmable parameters, inresponse to changes in the heart rate and hemodynamic state of thepatient.